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Topic: lead glass (Read 21863 times)

The blue fluorescence under shortwave UV seems to be a pretty good indicator of lead. I now personally believe that it's hard to say much at all about composition under longwave UV for either lead or non-lead, though it's possible that intense yellow green indicates manganese. However, a different color or absence of color doesn't necessarily mean the glass lacks manganese. As the link in my last reply says, "Manganese is one of the most difficult ions to deal with, because it absorbs and emits in the visible region. Previous workers have reported both green and red fluorescence and absorbtion peaks have been reported for the Mn2 ion at 355, 412, 418, 425, 430, 470 & 520 nm depending on the other glass constituents [2],[3],[4]. Fuxi reports Mn2 ion fluorescence at 526 & 606 nm. The Mn2 ion is only present in some glasses if they have been prepared under reducing conditions. The Mn3 ion has not been reported to fluoresce." (Italics mine.)

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Soda-type glasses (usually bottles and poor quality glass) often give no fluorescence probably due to the absence of a decoloriser.

Even cheap glass, if it doesn't have a greenish cast, most likely contains some kind of decolorant. There are many besides manganese: cerium, neodymium, cobalt, lead, arsenic, nickel and selenium are some of them, and sometimes they are used in combination. For instance, even lead glass may contain a decolorant besides lead. Choice depends on quantity and type of impurity, and conditions of the batch (e.g. whether it's reducing or oxidizing).

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Kristi

"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

I agree with your general contentions regarding lead fluorescence and the role of manganese although I have never seen a red fluorescence. The Manganic ion (Mn3) may well not fluoresce as you suggest since lead glasses generally require oxidising conditions. For this reason, arsenic and antimony oxides seem to be the usual decolorising additions to lead glasses, probably from about the middle of the 18th century. Incidentally, I found that Ravenscroft’s perfectly clear uncoloured crystal was made without added decoloriser due to the purity of his materials.

Re your statement: " There are many besides manganese: cerium, neodymium, cobalt, lead, arsenic, nickel and selenium are some of them, and sometimes they are used in combination."

The list of decolorisers you mention need to be considered on a time scale.

Manganese seems to have reigned supreme in both non-lead and lead glasses at least up to the end of the 18th century.

Antimony was certainly used as a decoloriser in antiquity and seems to have emerged, with arsenic, for decolorising lead glass in the 18th century and eventually replaced manganese for this purpose. In the 20th century their use has been kept secret in the UK apparently because of their poisonous nature affecting public opinion.

According to R. Wilkinson The Hallmarks of Antique Glass, 1968, nickel was used from c.1735 although I only ever found one later 18th century glass that might have been decolorised in this way. Cobalt (added in very small amounts on the “blue bag for washing” principle), found some use from the beginning of the 19th century. Both could be used in either type of glass.

Cerium and selenium were discovered by Berzelius in 1803 and 1817 respectively. I would be interested to know if either was much used before the 20th century. Cerium seems to have found its main use in blocking UV radiation in glasses for aircraft and solar cells etc. as well as a glass polish.Selenium on the other hand has, I understand, been much used in decolorising window glass and bottles of which there are classic American examples. Selenium is limited to non-lead glasses as its pink colour requires reducing conditions in the melt. At least in the early days, a problem with selenium was its low melting point with as much as 90% of the amount added to the batch being lost as toxic selenium vapour before completion of the founding process. I think this problem was eventually overcome by developing more stable selenium salts. Does anyone know the answer?

I suppose that, in theory, anything giving a pink colour could be used to balance the green colour of the ferrous (Fe2) iron. Neodymium would therefore quality, as would praseodymium, but neither was used in glass until 1923 when Moser first used neodymium to colour his non-lead glass pink. Due to its expense I doubt if it has ever found serious use as a decoloriser although perhaps you can tell me otherwise.

Erbium, discovered by Carl Gustaf Mosander in 1843, was until recently just a curiosity. However, it has become a commercially viable colorizer for glass due to its use in mobile phone components bringing down the price. It does give a pretty pink colour; but as a decoloriser . . .?

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Do you happen to know when manganese was phased out in Europe? It was used well into the 20th C here. I've seen purple glass that glows red, perhaps from manganese. Kind of odd, since the purple is from Mn3+. I imagine it might be due to the addition of another constituent. Mn is a strong modifier of fluorescence in many minerals. Cadmium + Mn perhaps? Or in this case, the orange glow could be from cadmium alone, rather than Mn, as suggested by the writer: http://reviews.ebay.com/FLUORESCENT-Glowing-MANGANESE-Glass-similar-to-Vaseline_W0QQugidZ10000000000103952

I wonder if sun-purple glass fluoresces less?

Neodymium was used quite extensively in Heisey glass, presumably as a decolorant. Quantities were small. Cost/benefit ratio would depend on how effective each decolorant is.

Thanks to Frank for explaining Quotes I will try it out sometime.krsilber asks a lot of questions which I will try to answer.

1. Regarding the demise of the use of Mn as a decoloriser I think (without hard evidence) that it continued in use well into the 20th century for non-lead glass. The following 1876 quote from Prof. Fredk. S. Barff, M.A. in British Manufacturing Industries, Ed G. Phillips Bevan F.G.S is interesting.:-“ ...The material employed was black oxide of manganese. This is still used in certain glass-works, but from its injurious action on the fire-clay pots, arsenious acid or common white arsenic is employed to the same effect.” It then goes on to describe the effect of sunlight on plate glass windows causing them to turn purple. This phenomenon is still visible in many banks of pavement lights around London, particularly when it has been raining and the new clear ones are clearly distinguishable.Do you remember the scandal some years back caused by “purpling” colorless Lalique car mascots using old hospital X-ray machines. It resulted in a big expensive court case in London.

2. The pictures on the first link do not look to me like Mn fluorescence but typical of cadmium/selenium much used in American red/yellow shaded glass. They may contain Mn as well but I do not think it is the cause of the fluorescence.

3. Sorry, I do not know about sun-purple glass in this respect. If you mean glass purplised by the sun I shall have to go out on a dark night and inspect a few pavements. My guess is not.

I read that neodymium is not a strong coloriser and would be required in some amount to act as a decoloriser. My guess is that this is an advertising ploy. Neodymium gives two strong black bands in the orange red region of the spectrum so you might be able to detect its presence with a hand spectroscope. I have just one piece of Heisey and that is 150 miles away at present!

Re neodymium; when I was in WheatonArts Glass Museum last spring I bought a large glass diamond with a pink colour. The label states that it is Tanznite glass but it shows the neodymium spectrum with my hand spectroscope. The interesting thing is that it turns a clear pale blue by our new light bulbs. In the UK we have just been made to abandon our old tungsten bulbs for new-style, long-life low-energy bulbs said to last 8 years!!! These look like tiny folded fluorescent tubes and have a complex spectrum with strong absorption at the red end. This change in the Tanznite diamond color does not occur with either a near or far UV lamp and, from its weight, I feel sure Tanznite is also a lead glass. This is different again from neodymium in (non-lead) Moser glass which does go from pink to blue under UV light.

Do you have these new-type bulbs in the US or elsewhere in the world?

4. I have looked up the effect of light on glass abstract and it says first “This study was restricted to soda-lime-silica glasses which contain various agents used as decolorizers in glass...” and then goes on to say ... “Glasses which contain antimony discolor less readily than similar arsenic-bearing glasses.” I could not find anything about lead glass. I presume that the stated distinction reflects the different redox properties of antimony and arsenic but don't ask me to explain that.

In a lead glass melt Mn color is very sensitive to oxygen concentration. Phelps Warren in "Irish Glass" cites a mid 18th century reference to color control by adding oxidising or reducing agents. A later reference that I cannot lay my hand on states that (my words) “ In the recent strike (1912) the glass left in the pots for several days turned pink.” This was attributed to the uptake of oxygen as the glass cooled. I have no experience of a direct sunlight effect on lead glass. See also my book "Glassmaking in London" for a more detailed explanaton.

5. The only thing I know about phosphate glasses is that they are slowly soluble inside a cow and therefore useful for the long term administration of drugs – sorry.

Fascinating discussion! I have a few pieces of orange Davidson Cloud which fluoresce an impressive orange/yellow under blacklight, due no doubt to the selenium/cadmium cullet used.

On point 3, it's a well known property of neodymium glass that it looks blue under fluorescent light and pink or purple under incandescent or sun light. If you search the board on neodymium or dichroic, you'll find more examples (and some great photographs illustrating the difference.) And in answer to your question, yes, we do have compact fluorescent lights in places other than Britain.

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David, you have a hand spectroscope?! Wow, I'm envious. That would be fun to play with.

1. Mn was commonly used in the US at least into the 1950s. I hadn't heard about the Lalique case, but sunpurple glass has been an ongoing issue here: some people collect it, so there's a market and a lot of it comes out of the southwest US, where people put it on their roofs or elsewhere outside to intentionally purple it. Many Early American Pattern Glass collectors think it a tragedy and a travesty (understandably, in my opinion).

I have a book of Heisey glass formulas that also has formulas from some other companies in it, and have gleaned much interesting info from that. Heisey used Mn in some of their lead and many lime glass formulas (though the amount of lead would not qualify it as "crystal" as defined in Europe). Neodymium was a common Heisey constituent in later years, found only in their colorless glasses (besides Alexandrite). It is also mentioned as a decolorant in the second link in my last reply, and I've seen it elsewhere. Its effects may have nothing to do with its coloring capacity, just as Mn isn't used as a decolorant because it can make purple.

2. I agree. I guess I wasn't clear enough about that before. So is the glow from selenium or cadmium or both? I thought it was the cadmium, but I suppose if selenium does it too, that might account for the orange glow seen in some colorless glass (especially Bohemian) if selenium was the decolorant. Pure speculation there.

3. We have CFBs, too. They come in regular and a more daylight-like spectrum. Makes me wonder how neodymium glass looks under different types of fluorescent bulbs

4. From that abstract: "Glasses which contain antimony discolor less readily than similar arsenic-bearing glasses, and cerium, lead, and iron oxides in sufficient amounts minimize the discoloration due to light"

I have to think more about electron exchange, color, Mn and Fe in a lead glass melt before saying anything here, or I’ll just make a fool of myself. Chemistry was always my least intuitive science. But I’m interested in this stuff, so it would be worthwhile to look into it more, and I appreciate your comments about it.

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Kristi

"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

Glad to hear that there are one or two others besides the UK helping to save the world by using these new bulbs!

Hi Cathy and krsilber, I have a small size Art Deco type orange Davidson vase which also glows as you say. And I have only just realised that it has a circuit of nine panels – how odd!Anyway, from testing a few other pieces I find that it is the orangey-yellow regions that fluoresce so I guess that cadmium is the culprit.

Glasses with the deep selenium red colour seems to vary under UV. Some have no response at all to either UV while others look as though they have a coating of dust on the surface. But a BIG discovery for me is that a 7-inch Whitefriars bud vase (with original label) does, in fact, have a clear red fluorescence. I had never thought to look at it before.

I suspect that these variations reflect the differing compositions of the batch used for selenium glass that, according to Weyl’s “Coloured glasses”, pub. Society of Glass Technology, can be very complex.

I have had my hand spectroscope for about 30 years. It is like a small telescope with a sliding focus but with a prism and variable slit replacing the objective lens (i.e. the one furthest from the eye). You can buy one on the web for UK£29, probably less in $. There are numerous sites on the web explaining how to make one from a CD although I think that is more difficult than it sounds. Looking out a cheap prism that gives a good spectrum would be a better bet.

I first learned about neodymium from Gary Baldwin’s book on Moser. The point I was trying to make is that while Moser’s neodymium Alexandrit does go from pink to blue under UV light the Tanznite diamond does not although it gives the neodymium spectrum. I have one other neodymium piece, Bohemian or Scandanavian, and that behaves like Tanznite. The common feature appears to be that both contain lead which Moser glass does not. More research is needed on this.

Herewith, in outline, my entirely new explanation of how Ravenscroft discovered English Lead Crystal Glass.

Lead in glass has a long history going back to antiquity. The earliest clear account after the Black Death of 1339 is a mid 16th century recipe book, possibly by Angelo Barovier, described by Moretti & Toninato, 2001, Ricette vetrarie del Rinascimento (translated by me from the Italian). Lead glass at that time was made by founding a mixture of lead oxide with ground flints.The resulting lead silicate was then used as the basis for other lead glasses, particularly false jewels, tesserae and enamels, but was generally too heavy for table ware, and it also had a yellow cast. This remained the basic lead glass on the continent up to and through the 17th century.

Peter Francis , in Apollo, tells us that in 1665 three glassmakers, da Costa, de Regnier and Odacio Formica worked together in Nijmegen (Holland) although there is no positive evidence that Formica was involved as he suggests. Da Costa probably made lead glass there as he emerges as a specialist in false jewels and bijouterie requiring high quality ingredients. There is no evidence that English lead crystal was invented there at that time as Francis suggests. His idea that a special new furnace was essential for the purpose is nonsense.

The three separated in 1668; five years later da Costa ends up in London where he has banker relatives. There is no evidence for an English lead crystal being made in the meantime. Francis tells us that da Costa built a furnace at the Savoy, in London and began making English lead crystal glass.

On the contrary, documentary evidence proves that George Ravenscroft set up the furnace for da Costa in 1673 and Robert Hooke , on a visit with Sir Christopher Wren, tells us that he was not making English lead crystal but “calcedonio”, described by Neri under the English name of “agates” because of its swirling colours.

Calcedonio is made by adding a complex prepared mixture of metal oxides etc. to best Venetian crystal further improved by the addition of the continental-style lead glass, all of which is described in detail in the above mid 16th century recipe book. Crucially, this addition of metal oxides is made not at the preparatory batch level but is stirred into the molten crystal glass to produce the swirling colours.

Working in England, da Costa used powdered flints because Hooke describes them among other materials. However he must have used some alternative ingredients as the Syrian soda, a monopoly in Venice, was not available. Also, following English practice to manage the new coal-fired furnace he would have included saltpetre (potassium nitrate) to protect the melt from smoke and fumes. Ravenscroft would have seen the proofs of the crystal taken to assess the readiness of the melt for the addition of the metallic salts and recognised that here was a glass of such quality as had never been seen before. Calcedonio was forgotten and he took out the well known patent on what was surely the crystal glass itself.

The problem with lead in glass is that under non-oxidising conditions molten metallic lead is formed and attacks and breaks the melting pots (See Neri). Ravenscroft was lucky in that the addition of saltpetre provided the oxidising conditions that prevented this happening. He was unlucky in that although da Costa’s modified lead crystal glass approximated to that of English lead crystal the amount of lead present (9% -15%) was not sufficient to prevent the glass from crizzling without the added metallic salts. It took a further two years, including the trial period, to overcome this problem, revealed in 1676 by the ring of the glass when struck and addition of his seal guarantee.

These events, and the time scale, prove that da Costa did not know in advance how to make English lead crystal glass. Francis and, possibly, Colin Brain (see Glass of the Alchemists, 2007, Corning Museum of Glass), nevertheless support the idea that English lead crystal was “invented” in Nijmegen. One reason for this is that a year after Ravenscroft had been awarded his patent in 1674 Formica applied for, and got, the same patent in Ireland. The most likely explanation is that he was told how to do it by his colleague, da Costa.

These are the facts and bones of the story as I believe them because they fit all the facts without exception. As always seemed unlikely for a merchant, Ravenscroft never undertook experiments to “invent” English lead crystal (stated without evidence for almost a century) at a time (1673) when the crystal glasshouse at Greenwich was said by John Evelyn to be making crystal glass as good if not better than that in Venice. It was a genuine case of “Chance favouring the prepared mind.” The key to the supreme quality of English lead crystal glass was that da Costa was using the very best batch materials available as used by makers of jewels, bijouterie etc.

Ravenscroft did not initially use his invention to make tableware but indulged in the more profitable market of making mirrors. He gave up his patent about the time that his partner in making mirror glasses, John Baker, died. The tableware industry seems to have been taken over by Hawley Bishopp in association with the Glass Sellers.

One of the truly great things about London is that there are people there who collect absolutely everything. One such site is Ghost London which has a section with fine illustrations of purplised pavement lights. With great authority we are even told that the purplisation is caused by ultraviolet light.To enjoy a quick browse of the site click Purple Pavement Lights

From that site you can link to the British Luxfer Prism Syndicate Limited, Founded in 1898 with an address at 16 Hill Street, Finsbury, London, E.C.2. Who apparently made or marketed at least some of these pavement lights.

Other firms are also mentioned including T. Hyatt & Co., 9 Farringdon Road, London, J.A. King & Co, 181 Queen Victoria Street, EC4., and a history of Hayward Bros. that had a factory in Southwark and, later Enfield. Pavement lights may have been a sidekick as it was apparently a foundry that made coal hole covers.

Regarding the origin of pavement lights a strong contender must be Professor Michael Faraday working at the Pellatt and Green factory in Southwark. It would seem that they were first invented to improve the internal lighting of ships. Ackerman's Repository, 1809 vol.1. relating to patent No. 3058 quotes two letters from ship's captains confirming the usefulness of the invention. I have not seen the patent so more info on this would be useful.

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